Fertilising guide
How to fertilise Frosty Fern (Selaginella kraussiana 'Frosty')— schedule & NPK
Also called Frosty fern, Frosty spikemoss, Krauss' spikemoss, African clubmoss, Spreading clubmoss.
More about frosty fern
About Frosty Fern
Selaginella kraussiana 'Frosty' · also called Frosty fern, Frosty spikemoss · houseplant
Frosty fern is a mat-forming spikemoss (not a true fern) prized for its lacy green fronds with frosted white tips. It demands constant moisture, high humidity and bright indirect light, making it a classic terrarium plant. The ASPCA lists it as non-toxic to cats, dogs and horses, so it is pet-safe.
Growth habit: Low, creeping, mat-forming evergreen with a fast growth rate; trailing rooting stems spread horizontally to form a dense carpet. New growth emerges bright white or cream (the "frosted" tips), maturing to green.
Watch for — Yellowing leaves: Often from excess fertiliser or too much light. Feed only at half strength monthly in the growing season and shade from direct sun.
What fertiliser frosty fern actually wants — and why
Frosty Fern is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for frosty fern: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed frosty fern, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For frosty fern:
Feed lightly about once a month during spring through autumn with a balanced liquid fertiliser diluted to half strength. Skip feeding in winter. Over-fertilising burns the delicate foliage and yellows the leaves, so err on the weak side. Treat that as once a month between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
The dormant-season rule matters more than the exact interval: skip feeding entirely when frosty fern is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for frosty fern
Half strength is the safe default for frosty fern — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
Feeding always goes onto already-damp soil, never dry roots — water frosty fern first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the frosty fern watering schedule.
Signs you are over-feeding frosty fern
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for frosty fern:
- Brown, crispy leaf tips and edges with no sign of underwatering.
- A white, crusty salt deposit on the soil surface or pot rim.
- Weak, pale, stretched new growth that flops.
- Lower leaves yellow and drop while the soil is correctly watered.
Signs you are under-feeding frosty fern
- Uniformly pale or yellow-green leaves, oldest first.
- Noticeably small new leaves and stalled growth in good light and season.
- A generally tired, lacklustre look despite correct watering and light.
If the symptoms point at watering, light or roots rather than nutrition, the full frosty fern care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of frosty fern with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Organic vs synthetic feeds for frosty fern
Organic options
A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.
Synthetic / liquid feeds
A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising frosty fern — frequently asked questions
What fertiliser does frosty fern need?
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Frosty Fern is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
How often should I feed frosty fern?
Feed lightly about once a month during spring through autumn with a balanced liquid fertiliser diluted to half strength. Skip feeding in winter. Over-fertilising burns the delicate foliage and yellows the leaves, so err on the weak side. Feed lightly about once a month during spring through autumn with a balanced liquid fertiliser diluted to half strength. Skip feeding in winter. Over-fertilising burns the delicate foliage and yellows the leaves, so err on the weak side. Treat that as once a month between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
What strength of feed for frosty fern?
Half strength is the safe default for frosty fern — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding frosty fern look like?
Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding frosty fern year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.
Should I flush the soil of frosty fern?
Flush the pot of frosty fern with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Keep reading
- Frosty Fern care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water frosty fern — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise snake plant
- How to fertilise dracaena
- How to fertilise peperomia
- All 569 fertilising guides in the Growli library